Taxol is a natural compound having the following chemical structure, which can be obtained in a small amount from a trunk or the like of Taxus brevifolia. ##STR2##
It is known that taxol has an antitumor activity and its action mechanism is based on the depolymerization inhibition action of microtubule during cell division, so that its clinical application is expected as an antitumor agent which is different from the general antitumor agents.
Though taxol can be obtained only in an extremely small amount from a natural source, reports have been published recently on the synthesis of taxol derivatives using a starting material 10-O-deacethylbaccatin III represented by the following structural formula: ##STR3## which is a taxol precursor that can be obtained in a relatively large amount from leaves and the like of taxaceous trees (cf. JP-A-3-505725; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Of such derivatives, a compound (Taxotere.TM.) represented by the following structural formula: ##STR4## has been drawing attention as a compound which has an antitumor activity similar to or higher than that of taxol and is now under development as an antitumor agent.
Though taxol and Taxotere.TM. are promising compounds as antitumor agents, their clinical tests have revealed that they have low efficacy on digestive organ cancers, especially large bowel cancers, so that great concern has been directed toward the development of a derivative having more strong antitumor effects.